When blades go wild

[webradbury]

I’m venting here so don’t mind me. But I hope I’m not the only one who has had trouble with knife blades during the forging/heat treating process. I get about a 60-70% success rate with blades not warping in the quench. Most times I can get the warp out during tempering with a trick I learned, but I spent too much time today trying to save a blade...and in the end, my trash can inherited it. The cutting edge was reflicted (a word my father invented), and the spine was the same but in the opposite way. This means I can straighten one and it throws the other out of line. So frustrating! I give up. Let’s go to the liquor store!  But seriously, I’ve learned that when a blade starts doing this, I don’t waste anymore time or energy on it, I count it as a loss and move on.

[Elnathan]

Last couple I've done I've heat-treated with the blades about 1/16" thicker than the intended final dimensions. That makes the final grind a fairly long operation and tedious operation, but warpage is generally minimal and if it occurs I have a bit of wiggle-room to straighten it out by favoring one side or the other in grinding.

Stress-relieving the blade after forging but prior to rough grinding, and then stress-relieving a second time prior to heat-treating may help with warping also. Mike Ameling used to do what he called thermal cycling of his fire strikers, a process of heating the piece up to successively lower temps and letting it cool to black heat in between heats, before hardening, and he swore that it dramatically reduced the number of strikers that broke in hardening. I've been loosely following that process and seems to work.

[Stoner creek]

Pre-heat your oil. Quench north to south. Quench in a cutting motion back and forth. Don’t quench in a stirring motion. I rarely get warpage using this method regardless of blade length or thickness. I learned that trick from a long-haired fellow from Woodbury.

[WH1]

agree on the preheating the oil.  What steel are you using?
not sure about the North/South thing but I do orient my quench bucket so I tend to do it
I also normalize (therma cycling)3 times prior to final heat and quench.  I have a magnet on my forge that I use to check for non magnetic prior to quench. 

[jcmcclure]

I preheat my oil, and quench in one of the old tall metal cracker boxes. I do not adhear to the north/south throught, but it would not hurt if you do. Joe Seabolt turned me onto and canola oil about a year ago and it has made life so much easier. I almost never have issues when using known steel, but is I occasionally make a file knife I notice that I will have a warp or two that need fixing.

[Joey R]

What Stoner said.

[lost arrow 801]

Pre-heat your oil. Quench north to south. Quench in a cutting motion back and forth. Don’t quench in a stirring motion. I rarely get warpage using this method regardless of blade length or thickness. I learned that trick from a long-haired fellow from Woodbury.

  that's great advice. I didn't buy it at first the north to south thing, but it works

[tippit]

I use Parks 50 oil...very fast.  I don't preheat Parks as it is likely to flare up.  In the past I've used Canola oil and then veterinary grade Mineral oil.  The only blade I've had problems with warping was my 4 sided ground long dagger.  That grind is a lot harder to keep symmetrical.  I think most of the warping comes from an uneven side to side symmetrical grind.  I grind to almost finish.

[LRB]

Last couple I've done I've heat-treated with the blades about 1/16" thicker than the intended final dimensions. That makes the final grind a fairly long operation and tedious operation, but warpage is generally minimal and if it occurs I have a bit of wiggle-room to straighten it out by favoring one side or the other in grinding.

Stress-relieving the blade after forging but prior to rough grinding, and then stress-relieving a second time prior to heat-treating may help with warping also. Mike Ameling used to do what he called thermal cycling of his fire strikers, a process of heating the piece up to successively lower temps and letting it cool to black heat in between heats, before hardening, and he swore that it dramatically reduced the number of strikers that broke in hardening. I've been loosely following that process and seems to work.

The heat cycling process is what gives you fine grain, making a stronger blade, but more than 3 cycles can make it difficult for the steel to harden as it should. With strikers as Mike was doing, a brine solution quench also helps to prevent breakage and cracks when quenching, although risky with thin knife blades. It is recommended in cycling to cool to almost room temp when using steels with .8% carbon or higher. Below .8% carbon, cooling to black is good enough. After forging it is best to anneal and then carry on to grinding, with a stress relief afterwards. Before the hardening quench is when to heat cycle, and all forged blades should be cycled to refine the grain. A blade from a file can be done by a simple low temp anneal called spherodizing  prior to shaping and stock removal if you don't need to forge a radical shape, because the grain size in a file is as good it gets. No harm if forged, but with stock removal all that is needed is a stress relief, hardening, and temper. Something to know in heat treating, is that non magnetic happens at 1414°F. The heat to quench should be about 60° higher with most steels. About two shades of red more. Also magnetic attraction after quench does not return until the blade temp drops to around 400°, so a north south quench would have no effect as far as magnetic induced warpage. I found that a point down quench reduces warpage. The main cause of warpage is uneven heat, and uneven cooling. Once a blade drops in temp to under 900°, they can often be straightened by hand. Once under 400°, not so much, but there are ways to straighten in the temper process.

[webradbury]

This blade was an old file since I ran out of my 1084 stock. I use a heat treat oven for temperature control and I preheat my quench oil. I'm sure my problem was a combination of a more difficult steel to HT and the number of times I reworked the blade trying to straighten it. This last time it wouldn't even harden. I'll stick to 1084 thank you! Thanks for the advise from everyone.

[Robby]

Thank you LRB, alway good to hear from you, especially on this subject!
Robby